1. Field of the Invention
The present invention relates to an ad hoc network system in which communication is performed between a predetermined number of terminals, and more particularly to a method for determining an optimal parent terminal and an ad hoc network system for the same.
2. Description of the Related Art
In a conventional ad hoc network, various methods are used to perform communication. One method is a parent wireless terminal intervening method in which an exclusive parent wireless terminal superior in processing capability to child wireless terminals is previously provided to form a network. Another method is a wireless terminal direct method in which synchronization is established each time data is transferred between wireless terminals which form the network. In the parent wireless terminal intervening method mentioned above, a wireless terminal located on an optimal communication position is selected as the parent wireless terminal. That is, the wireless terminal is selected as the parent wireless terminal such that all the child wireless terminals are contained in a communication region (service area) of the parent wireless terminal.
As a first conventional example of such a parent wireless terminal intervening communication system, a mobile wireless apparatus equipped with a function to support an optimal arrangement of a parent wireless terminal is disclosed in, for example, Japanese Laid Open Patent Disclosure (JP-A-Heisei 4-273638). In the first conventional example, a parent wireless terminal and each child wireless terminal are set to a test mode, and reception electric field strength between the parent wireless terminal and each child wireless terminal is measured in this test mode. The measurement result of this reception electric field strength is transmitted from each child wireless terminal to the parent wireless terminal. The parent wireless terminal can determine based on the measurement results that any child wireless terminal is impossible to use. Thus, the parent wireless terminal located on the optimal communication position is finally determined.
As a second conventional example of an ad hoc network system, a conference communication system is disclosed in Japanese Laid Open Patent Disclosure (JP-A-Heisei 4-367148). The conference communication system includes communication path allocating means for allocating a single wireless communication path to a plurality of child wireless terminals, and transmission status monitoring means for monitoring which of the child wireless terminals is transmitting on the single wireless communication line. Thereby, the child wireless terminals each having unexpensive and simple structures are allowed to perform conference communication.
Also, as a third conventional example, Japanese Laid Open Patent Disclosure (JP-A-Heisei 7-303280) is known. In the third conventional example, wireless terminals are subscribed to a network as a group, and communication limitation defining means is provided in a mobile wireless switch apparatus for group communication to define a simultaneous call limit for controlling traffic in the group. Thus, an ad hoc network is constructed.
In the first conventional example of the parent wireless terminal intervening communication system, because the measurement result of the reception electric field strength is transmitted from each child wireless terminal to the parent wireless terminal. As a result, any child wireless terminal which cannot be used is determined. However, this processing is complicated and takes a long time. Therefore, in the first conventional example, when the number of wireless terminals increases, there is the following problem. That is, the parent wireless terminal can not be selected for the plurality of child wireless terminal for a short time such that the parent wireless terminal is arranged on a communication position in a finally optimal service area.
Also, in the second conventional example of an ad hoc network, there is the following problem. That is, when the parent wireless terminal does not have a high data transmission rate, a transmission rate of the whole network is decreased due to a low transmission rate of a parent wireless terminal. Also, when the parent wireless terminal does not have an enough remaining battery power quantity, a communication line is disconnected because of power down in the parent wireless terminal.